While I think that it is quite historical that the AI will not essentially even think about negotiating for peace I am a little saddened by the fact that this will likely end up with a Finland in the same situation as in HOI3, namely that the Winter War cannot be won or even not lost in any way except for taking over the whole of Soviet Union, which is of course impossible.
I can imagine that a very well prepared, offensive Finland (which is of course quite unhistorical, I admit) could reasonably "win" the Winter War against the AI and take over the Kola peninsula, maybe even St Petersburg if the AI mucks up, and finally fortify down on a line from St Petersburg to the White Sea. In HOI3 this was quite doable and only ever actually helped the Soviet Union: Full on War Economy from 1939 made the Purge and the military and industrial buildup non-issues and made sure that Barbarossa would not get more than a couple of provinces inwards. Luckily in HOI3 this seems a little less likely as the high-end war laws require an opponent with more than 50 factories, we're told.
Still one might think, if Finland had managed to take over the Kola peninsula and fortify itself on a line that the Red Army could not breach, would the Soviets have kept trying to push through and enforce their demands on Finland? Or would they have suffered such a humiliation that they would've hoped to quietly get rid of the war, either by going back to Status Quo or by offering some limited concessions?
We cannot know as the idea is quite ridiculous in the real world but in the game I do hope that the AI won't just keep saying: "No no, we're obviously going to win this war."